Precise temporal and spatial regulation of gene expression is essential to many aspects of nervous system development, function and plasticity. Among several classes of gene regulatory factors, non-coding RNAs have emerged as a rich potential source of regulatory mechanism in the central nervous system. In particular, microRNAs (miRs) provide sequence-specific control over target mRNA translation and stability that can tune the levels of downstream proteins quite precisely thus improving the stability and robustness of molecular networks. However, comprehensive analysis of miR function within the intact nervous system has been very challenging, leaving open key questions such as: How complex is the miR regulatory landscape for neural circuits that mediate essential behaviors? Are these miRs acting mainly during neural development or are they reused to manage ongoing neural circuit activity and adaptation to stimuli? To what extent are miR mechanisms utilized in many parts of the brain, or do they regulate distinct sets of target genes in different cell types and/or developmental stages? In order to address these questions, we have assembled a team of accomplished investigators prepared to work in unison using multiple robust behavioral and cellular assays as part of an integrated program. Our team includes Drs. David Van Vactor (Harvard Medical School), Leslie Griffith (Brandeis University), Ronald Davis (Scripps Institute), and Dennis Wall (Stanford University), who will each assume responsibility for key components of this joint program. We will use Drosophila as a model organism that offers many sophisticated genetic tools complementary to the innovative tools we will develop. Drosophila has proven to be particularly effective for identification and dissection of cellular and molecular mechanisms underlying well conserved behaviors. This model is also accessible to a full range of techniques for determining the detailed cellular and physiological phenotypes of mutants in specific pathways, thus offering a system ideal for mapping out miR functions on a comprehensive scale followed by mechanistic dissection that will effectively leverage a wealth of tools and knowledge. Together, we will (i) build and apply new genetic tools, (ii) apply these tools to identify miRs required in multiple neural circuits, (iii) discover the mechanisms and regulatory strategies for miR function in each context, and then (iv) compare each model to distinguish general and specific strategies and examine their conservation. This will be the first analysis of its kind in the nervous system. Our preliminary findings already identify convergence between different circuits that will prioritize our detailed studies of several miRs: miR-13, miR-92, miR-190 and let-7. Preliminary analysis of miR-92 already points to a series of highly conserved downstream genes implicated in both neural circuit development and synaptic plasticity from insects to mammals, providing a set of specific mechanistic hypotheses that we will test in the three model circuits to define the regulatory logic for each validated target.